The nuclear lamina is a dense network of intermediate filaments beneath the inner nuclear membrane. Composed of A-type lamins (lamin A/C) and B-type lamins (lamins B1 and B2), the nuclear lamina provides a scaffold for the nuclear envelope and chromatin, thereby maintaining the structural integrity of the nucleus. A-type lamins are also found inside the nucleus where they interact with chromatin and participate in gene regulation. Viruses replicating in the cell nucleus have to overcome the nuclear envelope during the initial phase of infection and during the nuclear egress of viral progeny. Here, we focused on the role of lamins in the replication cycle of a dsDNA virus, mouse polyomavirus. We detected accumulation of the major capsid protein VP1 at the nuclear periphery, defects in nuclear lamina staining and different lamin A/C phosphorylation patterns in the late phase of mouse polyomavirus infection, but the nuclear envelope remained intact. An absence of lamin A/C did not affect the formation of replication complexes but did slow virus propagation. Based on our findings, we propose that the nuclear lamina is a scaffold for replication complex formation and that lamin A/C has a crucial role in the early phases of infection with mouse polyomavirus.

• Keywords
• VP1, lamin A/C, lamin B, mouse polyomavirus, viral replication centres,
• MeSH
• Cell Nucleus metabolism   virology   MeSH
• Phosphorylation MeSH
• Tumor Virus Infections virology   pathology   metabolism   genetics   MeSH
• Nuclear Lamina * metabolism   virology   MeSH
• Nuclear Envelope metabolism   virology   MeSH
• Lamin Type A * metabolism   genetics   MeSH
• Lamin Type B metabolism   genetics   MeSH
• Mice MeSH
• Polyomavirus Infections * virology   metabolism   genetics   pathology   MeSH
• Polyomavirus * genetics   pathogenicity   physiology   MeSH
• Virus Replication * MeSH
• Capsid Proteins metabolism   genetics   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Lamin Type A * MeSH
• Lamin Type B MeSH
• Capsid Proteins MeSH
• VP1 protein, polyomavirus MeSH Browser

At first glance the nucleus is a highly conserved organelle. Overall nuclear morphology, the octagonal nuclear pore complex, the presence of peripheral heterochromatin and the nuclear envelope appear near constant features right down to the ultrastructural level. New work is revealing significant compositional divergence within these nuclear structures and their associated functions, likely reflecting adaptations and distinct mechanisms between eukaryotic lineages and especially the trypanosomatids. While many examples of mechanistic divergence currently lack obvious functional interpretations, these studies underscore the malleability of nuclear architecture. I will discuss some recent findings highlighting these facets within trypanosomes, together with the underlying evolutionary framework and make a call for the exploration of nuclear function in non-canonical experimental organisms.

• Keywords
• Eukaryogenesis, Lamina, Lamins, Molecular evolution, Nuclear architecture, Nuclear envelope, Nuclear pore complex, Trypanosomes,
• MeSH
• Cell Nucleus metabolism   MeSH
• Nuclear Lamina metabolism   MeSH
• Nuclear Envelope metabolism   MeSH
• Nuclear Pore metabolism   MeSH
• Nuclear Pore Complex Proteins * MeSH
• Lamins metabolism   MeSH
• Evolution, Molecular MeSH
• Trypanosoma * metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Nuclear Pore Complex Proteins * MeSH
• Lamins MeSH

The nuclear lamina is the main component of the nuclear cytoskeleton that maintains the integrity of the nucleus. However, it represents a natural barrier for viruses replicating in the cell nucleus. The lamina blocks viruses from being trafficked to the nucleus for replication, but it also impedes the nuclear egress of the progeny of viral particles. Thus, viruses have evolved mechanisms to overcome this obstacle. Large viruses induce the assembly of multiprotein complexes that are anchored to the inner nuclear membrane. Important components of these complexes are the viral and cellular kinases phosphorylating the lamina and promoting its disaggregation, therefore allowing virus egress. Small viruses also use cellular kinases to induce lamina phosphorylation and the subsequent disruption in order to facilitate the import of viral particles during the early stages of infection or during their nuclear egress. Another component of the nuclear cytoskeleton, nuclear actin, is exploited by viruses for the intranuclear movement of their particles from the replication sites to the nuclear periphery. This study focuses on exploitation of the nuclear cytoskeleton by viruses, although this is just the beginning for many viruses, and promises to reveal the mechanisms and dynamic of physiological and pathological processes in the nucleus.

• Keywords
• adenovirus, baculovirus, circovirus, herpesvirus, lamin, nuclear actin, nuclear cytoskeleton, papillomavirus, parvovirus, polyomavirus,
• MeSH
• Actins metabolism   MeSH
• Cell Nucleus metabolism   MeSH
• Cytoskeleton genetics   metabolism   MeSH
• Species Specificity MeSH
• Host-Pathogen Interactions * MeSH
• Nuclear Lamina metabolism   MeSH
• Nuclear Envelope metabolism   MeSH
• Lamins metabolism   MeSH
• Humans MeSH
• Disease Susceptibility * MeSH
• Gene Expression Regulation, Viral MeSH
• Virus Replication MeSH
• Virus Diseases etiology   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Actins MeSH
• Lamins MeSH

The nuclear lamina supports many functions, including maintaining nuclear structure and gene expression control, and correct spatio-temporal assembly is vital to meet these activities. Recently, multiple lamina systems have been described that, despite independent evolutionary origins, share analogous functions. In trypanosomatids the two known lamina proteins, NUP-1 and NUP-2, have molecular masses of 450 and 170 kDa, respectively, which demands a distinct architecture from the ∼60 kDa lamin-based system of metazoa and other lineages. To uncover organizational principles for the trypanosome lamina we generated NUP-1 deletion mutants to identify domains and their arrangements responsible for oligomerization. We found that both the N- and C-termini act as interaction hubs, and that perturbation of these interactions impacts additional components of the lamina and nuclear envelope. Furthermore, the assembly of NUP-1 terminal domains suggests intrinsic organizational capacity. Remarkably, there is little impact on silencing of telomeric variant surface glycoprotein genes. We suggest that both terminal domains of NUP-1 have roles in assembling the trypanosome lamina and propose a novel architecture based on a hub-and-spoke configuration.

• Keywords
• Heterochromatin, Lamina, Macromolecular assembly, Nuclear organization, Trypanosomatid,
• MeSH
• Cell Nucleus MeSH
• Nuclear Lamina * genetics   MeSH
• Nuclear Envelope MeSH
• Lamins genetics   MeSH
• Telomere MeSH
• Trypanosoma * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Lamins MeSH

Differentiated nuclei can be reprogrammed/remodelled to totipotency after their transfer to enucleated metaphase II (MII) oocytes. The process of reprogramming/remodelling is, however, only partially characterized. It has been shown that the oocyte nucleus (germinal vesicle - GV) components are essential for a successful remodelling of the transferred nucleus by providing the materials for pseudo-nucleus formation. However, the nucleus is a complex structure and exactly what nuclear components are required for a successful nucleus remodelling and reprogramming is unknown. Till date, the only nuclear sub-structure experimentally demonstrated to be essential is the oocyte nucleolus (nucleolus-like body, NLB). In this study, we investigated what other GV components might be necessary for the formation of normal-sized pseudo-pronuclei (PNs). Our results showed that the removal of the GV nuclear envelope with attached chromatin and chromatin-bound factors does not substantially influence the size of the remodelled nuclei in reconstructed cells and that their nuclear envelopes seem to have normal parameters. Rather than the insoluble nuclear lamina, the GV content, which is dissolved in the cytoplasm with the onset of oocyte maturation, influences the characteristics and size of transferred nuclei.

• Keywords
• Nucleus transfer, Oocyte, Selective enucleation,
• MeSH
• Cell Nucleolus metabolism   MeSH
• Cell Nucleus metabolism   MeSH
• Chromatin metabolism   MeSH
• Cytoplasm metabolism   MeSH
• Nuclear Lamina metabolism   MeSH
• Nuclear Envelope metabolism   MeSH
• RNA, Messenger metabolism   MeSH
• Mice MeSH
• Oocytes cytology   metabolism   MeSH
• Oogenesis MeSH
• Ovarian Follicle metabolism   MeSH
• Cellular Reprogramming * MeSH
• Nuclear Transfer Techniques * MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chromatin MeSH
• RNA, Messenger MeSH

The organization of the nuclear periphery is crucial for many nuclear functions. Nuclear lamins form dense network at the nuclear periphery and play a substantial role in chromatin organization, transcription regulation and in organization of nuclear pore complexes (NPCs). Here, we show that TPR, the protein located preferentially within the nuclear baskets of NPCs, associates with lamin B1. The depletion of TPR affects the organization of lamin B1 but not lamin A/C within the nuclear lamina as shown by stimulated emission depletion microscopy. Finally, reduction of TPR affects the distribution of NPCs within the nuclear envelope and the effect can be reversed by simultaneous knock-down of lamin A/C or the overexpression of lamin B1. Our work suggests a novel role for the TPR at the nuclear periphery: the TPR contributes to the organization of the nuclear lamina and in cooperation with lamins guards the interphase assembly of nuclear pore complexes.

• Keywords
• Image analysis, Lamina, Lamins, Nuclear pore complex, Nucleus, Super-resolution imaging, TPR, Translocated promoter region,
• MeSH
• HeLa Cells MeSH
• Nuclear Lamina metabolism   ultrastructure   MeSH
• Nuclear Envelope metabolism   ultrastructure   MeSH
• Nuclear Pore Complex Proteins antagonists & inhibitors   genetics   metabolism   MeSH
• Lamin Type A antagonists & inhibitors   genetics   metabolism   MeSH
• Lamin Type B genetics   metabolism   MeSH
• Humans MeSH
• RNA, Small Interfering genetics   metabolism   MeSH
• Molecular Imaging MeSH
• Proto-Oncogene Proteins antagonists & inhibitors   genetics   metabolism   MeSH
• Gene Expression Regulation MeSH
• Signal Transduction MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Nuclear Pore Complex Proteins MeSH
• Lamin Type A MeSH
• Lamin Type B MeSH
• LMNA protein, human MeSH Browser
• RNA, Small Interfering MeSH
• Proto-Oncogene Proteins MeSH
• TPR protein, human MeSH Browser

The replication of the genome is a highly organized process, both spatially and temporally. Although a lot is known on the composition of the basic replication machinery, how its activity is regulated is mostly unknown. Several chromatin properties have been proposed as regulators, but a potential role of the nuclear DNA position remains unclear. We made use of the prominent structure and well-defined heterochromatic landscape of mouse pericentric chromosome domains as a well-studied example of late replicating constitutive heterochromatin. We established a method to manipulate its nuclear position and evaluated the effect on replication timing, DNA compaction and epigenetic composition. Using time-lapse microscopy, we observed that constitutive heterochromatin, known to replicate during late S-phase, was replicated in mid S-phase when repositioned to the nuclear periphery. Out-of-schedule replication resulted in deficient post-replicative maintenance of chromatin modifications, namely silencing marks. We propose that repositioned constitutive heterochromatin was activated in trans according to the domino model of origin firing by nearby (mid S) firing origins. In summary, our data provide, on the one hand, a novel approach to manipulate nuclear DNA position and, on the other hand, establish nuclear DNA position as a novel mechanism regulating DNA replication timing and epigenetic maintenance.

• MeSH
• Cell Nucleus genetics   ultrastructure   MeSH
• Cell Line MeSH
• DNA analysis   MeSH
• Heterochromatin * MeSH
• Histone Code * MeSH
• Histones metabolism   MeSH
• Nuclear Lamina ultrastructure   MeSH
• Nuclear Pore ultrastructure   MeSH
• Methylation MeSH
• Mice MeSH
• DNA Replication Timing * MeSH
• S Phase genetics   MeSH
• Gene Silencing MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA MeSH
• Heterochromatin * MeSH
• Histones MeSH

The nuclear lamina represents a multifunctional platform involved in such diverse yet interconnected processes as spatial organization of the genome, maintenance of mechanical stability of the nucleus, regulation of transcription and replication. Most of lamina activities are exerted through tethering of lamina-associated chromatin domains (LADs) to the nuclear periphery. Yet, the lamina is a dynamic structure demonstrating considerable expansion during the cell cycle to accommodate increased number of LADs formed during DNA replication. We analyzed dynamics of nuclear growth during interphase and changes in lamina structure as a function of cell cycle progression. The nuclear lamina demonstrates steady growth from G1 till G2, while quantitative analysis of lamina meshwork by super-resolution microscopy revealed that microdomain organization of the lamina is maintained, with lamin A and lamin B microdomain periodicity and interdomain gap sizes unchanged. FRAP analysis, in contrast, demonstrated differences in lamin A and B1 exchange rates; the latter showing higher recovery rate in S-phase cells. In order to further analyze the mechanism of lamina growth in interphase, we generated a lamina-free nuclear envelope in living interphase cells by reversible hypotonic shock. The nuclear envelope in nuclear buds formed after such a treatment initially lacked lamins, and analysis of lamina formation revealed striking difference in lamin A and B1 assembly: lamin A reassembled within 30 min post-treatment, whereas lamin B1 did not incorporate into the newly formed lamina at all. We suggest that in somatic cells lamin B1 meshwork growth is coordinated with replication of LADs, and lamin A meshwork assembly seems to be chromatin-independent process.

• Keywords
• Cell cycle, DNA replication, Interphase, Microdomains, Nuclear lamina, Nucleus,
• MeSH
• Cricetulus MeSH
• Interphase * MeSH
• Nuclear Lamina chemistry   metabolism   MeSH
• Cells, Cultured MeSH
• Humans MeSH
• Mice MeSH
• Swine MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

We investigated concerted evolution of rRNA genes in multiple populations of Tragopogon mirus and T. miscellus, two allotetraploids that formed recurrently within the last 80 years following the introduction of three diploids (T. dubius, T. pratensis, and T. porrifolius) from Europe to North America. Using the earliest herbarium specimens of the allotetraploids (1949 and 1953) to represent the genomic condition near the time of polyploidization, we found that the parental rDNA repeats were inherited in roughly equal numbers. In contrast, in most present-day populations of both tetraploids, the rDNA of T. dubius origin is reduced and may occupy as little as 5% of total rDNA in some individuals. However, in two populations of T. mirus the repeats of T. dubius origin outnumber the repeats of the second diploid parent (T. porrifolius), indicating bidirectional concerted evolution within a single species. In plants of T. miscellus having a low rDNA contribution from T. dubius, the rDNA of T. dubius was nonetheless expressed. We have apparently caught homogenization of rDNA repeats (concerted evolution) in the act, although it has not proceeded to completion in any allopolyploid population yet examined.

• MeSH
• Chromosomes, Plant MeSH
• Diploidy MeSH
• DNA, Plant MeSH
• Genome, Plant MeSH
• Genes, rRNA MeSH
• In Situ Hybridization, Fluorescence MeSH
• Nuclear Matrix chemistry   MeSH
• Evolution, Molecular * MeSH
• Molecular Sequence Data MeSH
• Polymorphism, Single-Stranded Conformational MeSH
• Polyploidy * MeSH
• Genetics, Population MeSH
• Restriction Mapping MeSH
• DNA, Ribosomal genetics   MeSH
• Seeds growth & development   MeSH
• Tragopogon cytology   genetics   growth & development   MeSH
• Geography MeSH
• Publication type
• Journal Article MeSH
• Comparative Study MeSH
• Names of Substances
• DNA, Plant MeSH
• DNA, Ribosomal MeSH

Three orthologous genes encoding programmed cell death 2 (PDCD2), TATA-binding protein (TBP), and proteasomal subunit C5 (PSMB1) proteins have been shown previously to be nonrandomly distributed in both mammalian and invertebrate genomes. Here we analyze a conserved synteny of the PDCD2, TBP, and PSMB1 orthologs in four nonmammalian vertebrates. Homologous genes of the chicken, zebrafish, fugu, and Tetraodon nigroviridis were identified. A chicken cosmid harboring the orthologs of these three genes was completely sequenced. The fish genes were analyzed in silico. In all seven vertebrates thus far investigated, the PDCD2 and TBP genes are located tail-to-tail. In six tested species but the zebrafish, the PSMB1 gene mapped head-to-head or in the close vicinity to the TBP, but even in the zebrafish, all three genes were syntenic. In contrast, a three times reused synteny breakpoint in the 5'-region from PDCD2 was detected. A comparative analysis revealed the distribution of putative matrix-attached regions (MARs), which may affect the synteny conservation.

• MeSH
• Cysteine Endopeptidases genetics   MeSH
• Zebrafish genetics   MeSH
• DNA chemistry   genetics   MeSH
• Nuclear Matrix metabolism   MeSH
• Cosmids genetics   MeSH
• Chickens genetics   MeSH
• Chromosome Mapping MeSH
• Molecular Sequence Data MeSH
• Vertebrates genetics   MeSH
• Polymorphism, Genetic MeSH
• TATA-Box Binding Protein genetics   MeSH
• Proteins genetics   MeSH
• Avian Proteins genetics   MeSH
• Replication Origin genetics   MeSH
• Sequence Analysis, DNA MeSH
• Synteny MeSH
• Takifugu genetics   MeSH
• Tetraodontiformes genetics   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Comparative Study MeSH
• Names of Substances
• Cysteine Endopeptidases MeSH
• DNA MeSH
• proteasome component C5 MeSH Browser
• TATA-Box Binding Protein MeSH
• Proteins MeSH
• Avian Proteins MeSH